MEGARA Pipeline

Overview

MEGARA (Multi-Espectrografo en GTC de Alta Resolucion para Astronomia) is an optical IFU and multi-object spectrograph on the 10.4 m Gran Telescopio Canarias (GTC). It features a hexagonal fiber bundle of 623 fibers covering a 12.5” x 11.3” field of view, with fiber core diameter of 0.62”.

3DCubeGen provides a complete pipeline for MEGARA that integrates the numina / megaradrp Data Reduction Pipeline (DRP) with the kernel interpolation cube reconstruction.

CLI Entry Point

The MEGARA pipeline is accessed via the pipemegara command:

pipemegara <command> [options]

Two commands are available:

Command	Purpose
`rundrp`	Manual step-by-step DRP execution + cube reconstruction
`runfulldrp`	Fully automated pipeline: sort observations, reduce calibrations, calibrate science data, and reconstruct cubes

rundrp

The rundrp command runs the MEGARA DRP reduction steps individually and then reconstructs a data cube. It requires the numina framework to be installed and the MEGARA DRP configuration files (obsresult-*.yaml, requirements-*.yaml) to be present in the working directory.

The reduction follows this calibration chain:

Bias – master bias creation
Traces – fiber trace identification
Wavelength calibration – arc lamp wavelength solution
Fiber flat – fiber-to-fiber response correction
Standard star – spectrophotometric calibration
Science – final science frame reduction + cube reconstruction

pipemegara rundrp --redux_dir /path/to/data --stdar_t HD12345 --vph LR-R

Key options:

Option	Default	Description
`-o, --out_path`	`out_cubes`	Output directory for the final cube
`-r, --redux_dir`	`''`	Path to the working directory with raw data
`-s, --sigm_s`	`0.35`	Smoothing kernel size (arcsec)
`-p, --pix_s`	`0.0`	Spaxel size (0 = same as `sigm_s`)
`-a, --alph_s`	`2.0`	Kernel shape factor
`-m, --stdar_t`	–	Name of the spectrophotometric standard star
`-y, --vph`	`LR-R`	VPH grating name (e.g., LR-B, LR-R, LR-Z, MR-R, HR-R)
`-u, --aper_std`	`4.0`	Aperture radius for spectrophotometric calibration (arcsec)
`-b, --basename`	`megCube-NAME.fits`	Output cube basename template

runfulldrp

The runfulldrp command automates the entire reduction workflow. It:

Sorts observation files by type (bias, arc, flat, standard, science)
Generates the DRP configuration files automatically
Runs all calibration steps
Performs spectrophotometric calibration iteratively
Reconstructs the final data cube
Extracts a 1D spectrum

It can be driven by CLI options or by a YAML configuration file.

pipemegara runfulldrp -c config_runfulldrp.yml

# Or with CLI options:
pipemegara runfulldrp --run_name GTC5-24AMEX --run_number 0001 \
    --obrun_path /path/to/raw --redux_path /path/to/redux \
    --out_path /path/to/output

Key additional options:

Option	Default	Description
`-t, --run_name`	`GTC5-24AMEX`	Name of the GTC observation run
`-g, --run_number`	`0001`	Observation block number (string format)
`-m, --obrun_path`	`''`	Path to the raw observation data
`-r, --redux_path`	`''`	Working directory for intermediate reduction products
`-c, --config_file`	`''`	Path to YAML config file (overrides CLI options)
`-e, --forcear`	`False`	Force use of ThAr arc lamp for wavelength calibration

Configuration File

The runfulldrp command accepts a YAML configuration file. A template is provided at CubeGen/megaratools/configfiles/config_runfulldrp.yml:

---
run_drp:
  - pipe_type: FULL
    run_name: GTC5-24AMEX
    run_number: '0001'
    out_path: out_cubes
    redux_ver: 1.1.1.dev0
    redux_path: ''
    obrun_path: ''
    sigm_s: 0.35
    pix_s: 0.0
    alph_s: 2.0
    flu16: True
    name: None
    basename: megCube-NAME.fits
    fac_sizey: 1.0
    fac_sizex: 1.0
    aper_std: 4.0
    forcear: False

Differences from LVM

While MEGARA uses the same core kernel interpolation algorithm, several defaults and behaviors differ:

Aspect	MEGARA	LVM
Default `sigm_s`	0.35” (sub-arcsecond)	32.2” (wide fibers)
`pix_s` when 0	Same as `sigm_s`	`0.75 * sigm_s`
Fiber geometry	623 fibers, hexagonal, 0.62” core	~1800 science fibers, 35.3” pitch
VPH selection	Multiple gratings (LR-B/R/Z, MR, HR)	N/A (fixed spectral range)
Spectrophotometric cal	Built into pipeline (iterative)	External (pre-calibrated SFrames)
DRP integration	Runs `numina` + `megaradrp`	Reads pre-reduced RSS frames